Heat exchanger

ABSTRACT

A heat exchanger includes two header tanks and a plurality of heat exchange tubes. The header tanks each include an outside plate, an inside plate, and an intermediate plate. The outside plate has an outwardly bulging portion(s). The inside plate has a plurality of tube insertion holes. The intermediate plate has communication holes for allowing communication of the tube insertion holes with the outwardly bulging portion of the header tank. A pair of inclined portions inclined in a fanning-out fashion toward the inside plate are formed at inside-plate-side edge portions of opposite wall surfaces of each communication hole which extend in the hole-length direction. Projecting portions of the inside plate are formed by bending, toward the intermediate plate, portions of the inside plate located at opposite edges of each tube insertion hole which extend in the hole-length direction. The projecting portions are closely brazed to the corresponding inclined portions.

BACKGROUND OF THE INVENTION

The present invention relates to a heat exchanger, and more particularly to a heat exchanger that can be favorably used as a gas cooler or an evaporator of a supercritical refrigeration cycle in which a CO₂ (carbon dioxide) refrigerant or a like supercritical refrigerant is used.

Herein and in the appended claims, the term “aluminum” encompasses aluminum alloys in addition to pure aluminum. Furthermore, herein and in the appended claims, the term “supercritical refrigeration cycle” means a refrigeration cycle in which a refrigerant on the high-pressure side is in a supercritical state; i.e., assumes a pressure in excess of a critical pressure. The term “supercritical refrigerant” means a refrigerant used in a supercritical refrigeration cycle.

A conventionally known heat exchanger for use in a supercritical refrigeration cycle includes a pair of header tanks disposed apart from each other; flat heat exchange tubes disposed in parallel at intervals between the two header tanks and having opposite end portions connected to the respective header tanks; and fins disposed in respective air-passing clearances between the adjacent heat exchange tubes (refer to Japanese Patent Application Laid-Open (kokai) No. 2005-300135). Each of the two header tanks is configured such that an outside plate, an inside plate, and an intermediate plate intervening between the outer and inside plates are brazed together in layers. The outside plate has an outwardly bulging portion extending in the longitudinal direction thereof and having an opening closed by the intermediate plate. The inside plate has a plurality of tube insertion holes in the form of through-holes formed in a region corresponding to the outwardly bulging portion of the outside plate and spaced apart from one another along the longitudinal direction thereof. The intermediate plate has a plurality of communication holes substantially larger than the tube insertion holes of the inside plate and in the form of through-holes formed for allowing the respective tube insertion holes to communicate with the interior of the outwardly bulging portion of the outside plate. Opposite end portions of the heat exchange tubes are inserted through the respective tube insertion holes of the inside plates and into the respective communication holes of the intermediate plates of the two header tanks. The entire outer peripheral surfaces of opposite end portions of the heat exchange tubes are brazed to the respective entire peripheral wall surfaces of the tube insertion holes of the inside plates of the two header tanks.

According to the heat exchanger described in the above publication, the communication holes formed in the intermediate plate are substantially larger than the tube insertion holes of the inside plate. Additionally, while opposite end portions of the heat exchange tubes are inserted through the respective tube insertion holes of the inside plates and into the respective communication holes of the intermediate plates of the two header tanks, the entire outer peripheral surfaces of opposite end portions of the heat exchange tubes are brazed to the respective entire peripheral wall surfaces of the tube insertion holes of the inside plates of the two header tanks. Thus, the inside plates have regions which face the communication holes of the intermediate plates and are not brazed to the intermediate plates. Therefore, this heat exchanger is usually sufficient in terms of withstand pressure in application to a gas cooler or an evaporator of a supercritical refrigeration cycle, but may fail to meet a demand, should it arise, for further enhancement in withstand pressure.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the above problem and to provide a heat exchanger which is further enhanced in terms of withstand pressure.

To fulfill the above object, the present invention comprises the following modes.

1) A heat exchanger comprising a pair of header tanks disposed apart from each other and a plurality of flat heat exchange tubes disposed in parallel at intervals between the two header tanks and having opposite end portions connected to the respective header tanks, each of the two header tanks being configured such that an outside plate, an inside plate, and an intermediate plate intervening between the outside and inside plates are brazed together in layers, the outside plate having an outwardly bulging portion extending in a longitudinal direction thereof and having an opening closed by the intermediate plate, the inside plate having a plurality of tube insertion holes in the form of through-holes formed in a region corresponding to the outwardly bulging portion of the outside plate and spaced apart from one another along a longitudinal direction thereof, and the intermediate plate having a plurality of communication holes in the form of through-holes formed for allowing the respective tube insertion holes of the inside plate to communicate with the interior of the outwardly bulging portion of the outside plate,

wherein a pair of inclined portions inclined in a fanning-out fashion toward the inside plate are formed at inside-plate-side edge portions of opposite wall surfaces of each communication hole of the intermediate plate which extend in a hole-length direction of the communication hole;

a pair of projecting portions projecting toward the intermediate plate are formed on a surface of the inside plate which faces the intermediate plate, the projecting portions being located at positions corresponding to opposite edges of each tube insertion hole which extend in a hole-length direction of the tube insertion hole and being in close contact with the corresponding inclined portions of the intermediate plate; and

the projecting portions are brazed to the corresponding inclined portions.

2) A heat exchanger according to par. 1), wherein opposite end portions of the heat exchange tubes are inserted through the respective tube insertion holes of the inside plates and into the respective communication holes of the intermediate plates of the two header tanks; entire outer peripheral surfaces of opposite end portions of the heat exchange tubes are brazed to the respective entire peripheral wall surfaces of the tube insertion holes of the inside plates; and at least opposite-side surfaces, extending in a tube-width direction, of the entire outer peripheral surfaces of opposite end portions of the heat exchange tubes and at least opposite wall surfaces, extending in the hole-length direction, of the entire peripheral wall surfaces of the communication holes of the intermediate plates are respectively brazed together.

3) A heat exchanger according to par. 1), wherein a hole width of the tube insertion hole of the inside plate and a hole width of the communication hole of the intermediate plate are equal.

4) A heat exchanger according to par. 1), wherein Wp≦(Wt+0.8) and Hp≦(Ht+0.3) are satisfied, where Wp (mm) is a dimension of the communication hole of the intermediate plate as measured in the hole-length direction, Hp (mm) is a dimension of the communication hole of the intermediate plate as measured in a hole-width direction, Wt (mm) is a tube width of the heat exchange tube, and Ht (mm) is a tube height of the heat exchange tube.

5) A heat exchanger according to par. 1), wherein the projecting portions of the inside plate are formed by bending, toward the intermediate plate, portions of the inside plate corresponding to opposite edges of each tube insertion hole which extend along in the hole-length direction of the tube insertion hole.

6) A heat exchanger according to par. 1), wherein stepped portions are formed on a peripheral wall surface of each communication hole of the intermediate plate to be located at opposite end portions of the communication hole with respect to the hole-length direction, the stepped portions projecting inward with respect to the hole-length direction and engaging an end surface of the corresponding heat exchange tube.

7) A heat exchanger according to par. 6), wherein a projecting height of each stepped portion of the intermediate plate from the peripheral wall surface of the corresponding communication hole is determined so as not to cover a refrigerant channel of the corresponding heat exchange tube.

8) A heat exchanger according to par. 1), wherein each heat exchange tube is brazed to a peripheral wall surface of the communication hole of the intermediate plate by use of a brazing material on an outer peripheral surface of the heat exchange tube.

9) A heat exchanger according to par. 8), wherein the heat exchange tube comprises a pair of flat walls facing each other and two side walls each extending between opposed side edges of the two flat walls and is formed by bending a tube-forming sheet-like member in the form of an aluminum brazing sheet having a brazing material layer on each of opposite sides.

According to the heat exchanger of par. 1), a pair of inclined portions inclined in a fanning-out fashion toward the inside plate are formed at inside-plate-side edge portions of opposite wall surfaces of each communication hole of the intermediate plate which extend in a hole-length direction of the communication hole; a pair of projecting portions projecting toward the intermediate plate are formed on a surface of the inside plate which faces the intermediate plate, the projecting portions being located at positions corresponding to opposite edges of each tube insertion hole which extend in a hole-length direction of the tube insertion hole and being in close contact with the corresponding inclined portions of the intermediate plate; and the projecting portions are brazed to the corresponding inclined portions. Thus, the brazed area between the inside plates and the respective intermediate plates becomes greater than that in the above-mentioned heat exchanger described in Japanese Patent Application Laid-Open (kokai) No. 2005-300135, thereby increasing withstand pressure of portions around the tube insertion holes of the inside plates. This enhances, in terms of withstand pressure, the header tanks and the brazed regions between the inside plates and the heat exchange tubes. Furthermore, opposite end portions of the heat exchange tubes are restrained by the respective intermediate plates from opposite sides in a tube-height direction via the projecting portions of the inside plates which are brazed to the intermediate plates, thereby enhancing the heat exchange tubes in terms of withstand pressure in the tube-height direction. As a result, the entire heat exchanger is enhanced in terms of withstand pressure.

Since the projecting portions of the inside plates are in close contact with the respective inclined portions of the intermediate plates, in a tentatively assembled condition before brazing, a positional misalignment between the inner and intermediate plates can be prevented.

According to the heat exchanger of par. 2), at least opposite-side surfaces, extending in the tube-width direction, of the entire outer peripheral surfaces of opposite end portions of the heat exchange tubes and at least opposite wall surfaces, extending in the hole-length direction, of the entire peripheral wall surfaces of the communication holes of the intermediate plates are respectively brazed together. Thus, the brazed length between the heat exchange tubes and the header tanks becomes relatively long, thereby increasing brazing strength. As compared with the heat exchanger described in Japanese Patent Application Laid-Open (kokai) No. 2005-300135, the brazed zones between the heat exchange tubes and the header tanks are further enhanced in terms of withstand pressure. Since opposite end portions of the heat exchange tubes are restrained directly by the respective intermediate plates from opposite sides in the tube-height direction, the heat exchange tubes are also further enhanced in terms of withstand pressure in the tube-height direction.

According to the heat exchanger of par. 3), on the surface of the inside plate which faces the intermediate plate, opposite edge portions which extend along the tube insertion hole in the hole-length direction are free from a region which faces the communication hole and is not brazed to the intermediate plate. Accordingly, sufficiently high withstand pressure can be imparted to portions of the inside plate around the tube insertion holes, so that the header tanks and the brazed zones between the inside plates and the heat exchange tubes are further enhanced in terms of withstand pressure.

According to the heat exchanger of par. 4), Wp and Hp are set to the respective ranges mentioned above. This ensures a brazed area between the inside plate and the intermediate plate required to exhibit a minimum necessary withstand pressure even when, on the surface of the inside plate which faces the intermediate plate, opposite edge portions which extend along the tube insertion hole in the hole-length direction have a region which faces the communication hole and is not brazed to the intermediate plate.

The heat exchanger of par. 5) allows relatively easy formation of the projecting portions of the inside plate. Furthermore, portions of the surface of the inside plate on a side opposite the intermediate plate, which correspond to the opposite edges of each tube insertion hole with respect to the tube-height direction are resultantly inclined in a narrowing fashion toward the intermediate plate. In the course of insertion of end portions of the heat exchange tubes into the respective tube insertion holes in manufacture of the heat exchanger, the thus-formed inclined surfaces serve as guides, thereby facilitating insertion of the heat exchange tubes.

The heat exchanger of par. 6) allows the constant-depth insertion of end portions of the heat exchange tubes into an assembly of the three plates in the manufacture of the heat exchanger. Therefore, all of the heat exchange tubes are inserted to the same depth into the two header tanks of the heat exchanger, thereby stabilizing divided flow of a refrigerant into all of the heat exchange tubes and enhancing heat-exchanging performance.

According to the heat exchanger of par. 7), an increase in flow resistance of a refrigerant is prevented.

The heat exchanger of par. 9) allows relatively easy brazing of the outer peripheral surfaces of opposite end portions of the heat exchange tubes to the respective peripheral wall surfaces of the tube insertion holes of the inside plates and to the respective peripheral wall surfaces of the communication holes of the intermediate plates by use of the brazing material layers of the tube-forming sheet-like members.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the overall construction of a gas cooler to which the heat exchanger according to the present invention is applied;

FIG. 2 is a fragmentary view in vertical section showing the gas cooler of FIG. 1 as it is seen frontward from rear;

FIG. 3 is a perspective view showing a first header tank of the gas cooler of FIG. 1;

FIG. 4 is an enlarged view in section taken along line A-A of FIG. 2;

FIG. 5 is an enlarged view in section taken along line B-B of FIG. 2;

FIG. 6 is an enlarged view in section taken along line C-C of FIG. 5;

FIG. 7 is an exploded perspective view showing a method of manufacturing the first header tank of the gas cooler of FIG. 1;

FIG. 8 is an exploded perspective view showing a method of manufacturing a second header tank of the gas cooler of FIG. 1;

FIG. 9 is a cross-sectional view showing a heat exchange tube of the gas cooler of FIG. 1;

FIG. 10 is a fragmentary enlarged view of FIG. 9;

FIG. 11 is a view showing a method of manufacturing the heat exchange tube shown in FIG. 9; and

FIG. 12 is a diagram showing the flow of a refrigerant through the gas cooler of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention will next be described in detail with reference to the drawings. This embodiment is implemented by applying a heat exchanger according to the present invention to a gas cooler of a supercritical refrigeration cycle.

In the following description, the upper, lower, left-hand, and right-hand sides of FIGS. 1 and 2 will be referred to as “upper,” “lower,” “left,” and “right,” respectively. Also, the downstream side of flow (represented by arrow X in FIG. 1) of air through air-passing clearances between adjacent heat exchange tubes will be referred to as the “front,” and the opposite side as the “rear.”

FIGS. 1 and 2 show the overall construction of a gas cooler to which the heat exchanger according to the present invention is applied. FIGS. 3 to 6 show the configuration of essential portions of the gas cooler of FIG. 1. FIGS. 7 and 8 show a method of manufacturing header tanks. FIGS. 9 and 10 show a heat exchange tube. FIG. 11 shows a method of manufacturing the heat exchange tube. FIG. 12 shows the flow of a refrigerant through the gas cooler of FIG. 1.

With reference to FIG. 1, a gas cooler 1 of a supercritical refrigeration cycle wherein a supercritical refrigerant, such as CO₂, is used includes two header tanks 2 and 3 extending vertically and spaced apart from each other in the left-right direction; a plurality of flat heat exchange tubes 4 arranged in parallel between the two header tanks 2 and 3 and spaced apart from one another in the vertical direction; corrugated fins 5 arranged in respective air-passing clearances between adjacent heat exchange tubes 4 and at the outside of the upper-end and lower-end heat exchange tubes 4 and each brazed to the adjacent heat exchange tubes 4 or to the upper-end or lower-end heat exchange tube 4; and side plates 6 of aluminum arranged externally of and brazed to the respective upper-end and lower-end corrugated fins 5. In the case of this embodiment, the header tank 2 at the right will be referred to as the “first header tank,” and the header tank 3 at the left as the “second header tank.”

As shown in FIGS. 2 to 6, the first header tank 2 is configured such that an outside plate 7, an inside plate 8, and an intermediate plate 9 intervening between the outside plate 7 and the inside plate 8 are brazed together in layers. The outside plate 7 and the inside plate 8 are each formed from a brazing sheet having a brazing material layer on each of opposite sides; herein, an aluminum brazing sheet. The intermediate plate 9 is formed from a bare metal material; herein, a bare aluminum material.

The outside plate 7 has a plurality of; herein, two, dome-like outwardly bulging portions 11A and 11B spaced apart from each other in the vertical direction. In the outside plate 7, a peripheral portion around a leftward-facing opening of each of the outwardly bulging portions 11A and 11B is brazed to the intermediate plate 9, whereby the intermediate plate 9 covers the leftward-facing openings of the outwardly bulging portions 11A and 11B. As a result, the interior of each of the outwardly bulging portions 11A and 11B serves as a refrigerant flow section whose upper and lower ends are closed. Those portions of the first header tank 2 which correspond to the outwardly bulging portions 11A and 11B serve as respective header sections.

A refrigerant inlet 12 is formed in a crest portion of the upper outwardly bulging portion 11A of the outside plate 7. An inlet member 13 of a metal; herein, a bare aluminum material, having a refrigerant inflow channel 14 in communication with the refrigerant inlet 12 is brazed to the outer surface of the outwardly bulging portion 11A by use of the brazing material on the outer surface of the outside plate 7. A refrigerant outlet 15 is formed in a crest portion of the lower outwardly bulging portion 11B. An outlet member 16 of a metal; herein, a bare aluminum material, having a refrigerant outflow channel 17 in communication with the refrigerant outlet 15 is brazed to the outer surface of the outwardly bulging portion 11B by use of the brazing material on the outer surface of the outside plate 7. The outside plate 7 is formed, by press work, from an aluminum brazing sheet having a brazing material layer on each of opposite sides.

A plurality of tube insertion holes 18 elongated in the front-rear direction are formed through the inside plate 8 and are vertically spaced apart from one another. An upper-half group of tube insertion holes 18 are formed within a vertical range corresponding to the upper outwardly bulging portion 11A of the outside plate 7. Similarly, a lower-half group of tube insertion holes 18 are formed within a vertical range corresponding to the lower outwardly bulging portion 11B. The tube insertion holes 18 have a front-to-rear length slightly longer than the front-to-rear width of the outwardly bulging portions 11A and 11B such that front and rear end portions thereof project outward beyond the front and rear ends, respectively, of the outwardly bulging portions 11A and 11B. Front and rear edge portions of the inside plate 8 have integrally formed respective cover walls 19. The cover walls 19 project rightward such that their ends reach the outer surface of the outside plate 7, and cover respective boundary portions between the outside plate 7 and the intermediate plate 9 along the overall length of the boundary portions. The cover walls 19 are brazed to the front and rear side surfaces, respectively, of the outside plate 7 and the intermediate plate 9. The projecting end of each of the cover walls 19 has a plurality of integrally formed engaging portions 21 which are vertically spaced apart from one another. The engaging portions 21 of the cover walls 19 are engaged with and brazed to the outer surface of the outside plate 7.

A pair of projecting portions 26 are integrally formed on the inside plate 8 at positions located at opposite sides of each tube insertion hole 18 with respect to the tube-height direction (vertical direction); i.e., at positions corresponding to opposite edges of each tube insertion hole 18 which extend in the hole-length direction. The projecting portions 26 project outward with respect to the left-right direction; i.e., toward the intermediate plate 7, via inclined portions which are slightly inclined toward the tube-insertion-hole-18 side and toward the intermediate plate 7 (outward with respect to the left-right direction). The projecting portions 26 are formed by bending portions of the inside plate 8 corresponding to the opposite edges of each tube insertion hole 18 outward with respect to the left-right direction. The vertically outer surfaces of the projecting portions 26 are inclined outward with respect to the left-right direction and toward the tube-insertion-hole-18 side. The inside plate 8 is formed, by press work, from an aluminum brazing sheet having a brazing material layer on each of opposite sides.

The intermediate plate 9 has communication holes 22 in the form of through-holes for allowing the tube insertion holes 18 of the inside plate 8 to communicate with the interiors of the outwardly bulging portions 11A and 11B and in a number equal to the number of the tube insertion holes 18. The communication holes 22 positionally coincide with the respective tube insertion holes 18 of the inside plate 8 and have the same width as the tube insertion holes 18. A pair of inclined portions 27 inclined in a vertically fanning-out fashion toward the inside plate 8 (to the left) are formed at edge portions of vertically opposite wall surfaces of each communication hole 22 of the intermediate plate 9 which extend in the hole-length direction, the edge portions being located on a side toward the inside plate 8 (inward edge portions with respect to the left-right direction). The inclined surfaces of the projecting portions 26 of the inside plate 8 are in close contact with and brazed to the respective inclined portions 27 of the intermediate plate 9. On the peripheral wall surface of the communication hole 22 of the intermediate plate 9, opposite end portions with respect to the hole-length direction (front and rear end portions) have respective stepped portions 25 which are located at an intermediate position with respect to the plate-thickness direction of the intermediate plate 9; which project inward with respect to the hole-length direction of the communication hole 22; and which an end surface of the heat exchange tube 4 abuts. The projecting height of the stepped portion 25 of the intermediate plate 9 from the peripheral wall surface of the communication hole 22 is determined so as not to cover a refrigerant channel 4 a, which will be described later, of the heat exchange tube 4. An upper-half group of tube insertion holes 18 of the inside plate 8 communicate with the interior of the upper outwardly bulging portion 11A via an upper-half group of respective communication holes 22 of the intermediate plate 9. Similarly, a lower-half group of tube insertion holes 18 communicate with the interior of the lower outwardly bulging portion 11B via a lower-half group of respective communication holes 22 of the intermediate plate 9. All of the communication holes 22 in communication with the interior of the upper outwardly bulging portion 11A communicate with one another via communication portions 23, and all of the communication holes 22 in communication with the interior of the lower outwardly bulging portion 11B communicate with one another via the communication portions 23. The communication portions 23 are formed by cutting off portions between the adjacent communication holes 22 in the intermediate plate 9. Thus, the intermediate plate 9 has a refrigerant flow section communicating with the interior of the outwardly bulging portion 11A, and a refrigerant flow section communicating with the interior of the outwardly bulging portion 11B. The intermediate plate 9 is formed, by press work, from a bare aluminum material.

Preferably, the relations Wp≦(Wt+0.8) and Hp≦(Ht+0.3) are satisfied, where Wp (mm) is a dimension of the communication hole 22 of the intermediate plate 9 as measured in the hole-length direction (front-rear direction), Hp (mm) is a dimension of the communication hole 22 of the intermediate plate 9 as measured in the hole-width direction (vertical direction), Wt (mm) is the tube width of the heat exchange tube 4, and Ht (mm) is the tube height (vertical thickness) of the heat exchange tube 4 (see FIGS. 4 and 6). In the case of Wp>(Wt+0.8) and Hp>(Ht+0.3), on the surface of the inside plate 8 which faces the intermediate plate 9, opposite edge portions which extend along the tube insertion hole 18 in the hole-length direction involves a region which faces the communication hole 22 and is not brazed to the intermediate plate 9. As a result, the brazed area between the inside plate 8 and the intermediate plate 9 becomes insufficient, potentially resulting in a failure to exhibit sufficient withstand pressure.

The second header tank 3 has substantially the same construction as the first header tank 2, and like features and parts are designated by like reference numerals (see FIG. 2). The two header tanks 2 and 3 are disposed such that the respective inside plates 8 face each other. The second header tank 3 differs from the first header tank 2 in that the outside plate 7 has dome-like outwardly bulging portions provided in a number one fewer than the outwardly bulging portions 11A and 11B of the first header tank 2; herein, a single dome-like outwardly bulging portion 24, which extends from an upper end portion to a lower end portion of the outside plate 7 and is opposed to the outwardly bulging portions 11A and 11B of the first header tank 2; the outwardly bulging portion 24 does not have a refrigerant inlet and a refrigerant outlet; all of the tube insertion holes 18 of the inside plate 8 communicate with the interior of the outwardly bulging portion 24 via all of the respective communication holes 22 of the intermediate plate 9; and all of the communication holes 22 of the intermediate plate 9 communicate with one another via the communication portions 23, which are formed by cutting off portions between the adjacent communication holes 22. The outwardly bulging portion 24 has the same bulging height and width as the outwardly bulging portions 11A and 11B of the first header tank 2. In the outside plate 7, a peripheral portion around a rightward-facing opening of the outwardly bulging portion 24 is brazed to the intermediate plate 9, whereby the intermediate plate 9 covers the rightward-facing opening of the outwardly bulging portion 24. As a result, the interior of the outwardly bulging portion 24 serves as a refrigerant flow section whose upper and lower ends are closed. A portion of the second header tank 3 which corresponds to the outwardly bulging portion 24 serves as a header section. All of the communication holes 22 and the communication portions 23 of the intermediate plate 9 form a refrigerant flow section communicating with the interior of the outwardly bulging portion 24.

The two header tanks 2 and 3 are manufactured as shown in FIGS. 7 and 8.

First, an aluminum brazing sheet having a brazing material layer on each of opposite sides is subjected to press work so as to form the outside plate 7 having the outwardly bulging portions 11A and 11B and the outside plate 7 having the outwardly bulging portion 24. The refrigerant inlet 12 and the refrigerant outlet 15 are formed in the outside plate 7 for the first header tank 2. Also, an aluminum brazing sheet having a brazing material layer on each of opposite sides is subjected to press work so as to form the inside plates 8 each having the tube insertion holes 18, the projecting portions 26, the cover walls 19, and engaging-portion-forming lugs 21A extending straight from the cover walls 19. Furthermore, a bare aluminum material is subjected to press work so as to form the intermediate plates 9 each having the communication holes 22, the inclined portions 27, the stepped portions 25, and the communication portions 23.

Next, the three plates 7, 8, and 9 are stacked such that the inclined surfaces of the projecting portions 26 of the inside plate 8 are in close contact with the respective inclined portions 27 of the intermediate plate 9. Subsequently, the lugs 21A are bent so as to form the engaging portions 21 engaged with the outside plate 7, thereby forming a provisional assembly. Subsequently, the provisional assemblies are heated at a predetermined temperature, whereby, by use of the brazing material layers of the outside plate 7 and the brazing material layers of the inside plate 8, the three plates 7, 8, and 9 are brazed together, the cover walls 19 and the front and rear end surfaces of the intermediate plate 9 and the outside plate 7 are brazed together, the projecting portions 26 and the respective inclined portions 27 are brazed together, and the engaging portions 21 and the outside plate 7 are brazed together. Thus are manufactured the two header tanks 2 and 3.

As shown in FIGS. 9 and 10, the heat exchange tube 4 includes mutually opposed flat upper and lower walls 31 and 32 (a pair of flat walls); front and rear side walls 33 and 34 which extend over front and rear side ends, respectively, of the upper and lower walls 31 and 32; and a plurality of reinforcement walls 35 which are provided at predetermined intervals between the front and rear side walls 33 and 34 and extend longitudinally and between the upper and lower walls 31 and 32. By virtue of this structure, the heat exchange tube 4 internally has a plurality of refrigerant channels 4 a arranged in the width direction thereof.

The front side wall 33 has a dual structure and includes an outer side-wall-forming elongated projection 36 which is integrally formed with the front side end of the upper wall 31 in a downward raised condition and extends along the entire height of the heat exchange tube 4; an inner side-wall-forming elongated projection 37 which is located inside the outer side-wall-forming elongated projection 36 and is integrally formed with the upper wall 31 in a downward raised condition; and an inner side-wall-forming elongated projection 38 which is integrally formed with the front side end of the lower wall 32 in an upward raised condition. The outer side-wall-forming elongated projection 36 is brazed to the two inner side-wall-forming elongated projections 37 and 38 and the lower wall 32 while a lower end portion thereof is engaged with a front side edge portion of the lower surface of the lower wall 32. The two inner side-wall-forming elongated projections 37 and 38 are brazed together while butting against each other. The rear side wall 34 is integrally formed with the upper and lower walls 31 and 32. A projection 38 a is integrally formed on the tip end face of the inner side-wall-forming projection 38 of the lower wall 32 and extends in the longitudinal direction of the inner side-wall-forming projection 38 along the entire length thereof. A groove 37 a is formed on the tip end face of the inner side-wall-forming elongated projection 37 of the upper wall 31 and extends in the longitudinal direction of the inner side-wall-forming elongated projection 37 along the entire length thereof. The projection 38 a is press-fitted into the groove 37 a.

The reinforcement walls 35 are formed such that reinforcement-wall-forming elongated projections 40 and 41, which are integrally formed with the upper wall 31 in a downward raised condition, and reinforcement-wall-forming elongated projections 42 and 43, which are integrally formed with the lower wall 32 in an upward raised condition, are brazed together while the reinforcement-wall-forming elongate projections 40 and 41 butt against the reinforcement-wall-forming elongated projections 43 and 42, respectively. The upper wall 31 has the reinforcement-wall-forming elongated projections 40 and 41, which are of different projecting heights and are arranged alternately in the front-rear direction. The lower wall 32 has the reinforcement-wall-forming elongated projections 42 and 43, which are of different projecting heights and are arranged alternately in the front-rear direction. The reinforcement-wall-forming elongated projections 40 of a long projecting height of the upper wall 31 and the respective reinforcement-wall-forming elongated projections 43 of a short projecting height of the lower wall 32 are brazed together. The reinforcement-wall-forming elongated projections 41 of a short projecting height of the upper wall 31 and the respective reinforcement-wall-forming elongated projections 42 of a long projecting height of the lower wall 32 are brazed together. Hereinafter, the reinforcement-wall-forming elongated projections 40 and 42 of a long projecting height of the upper and lower walls 31 and 32 are called the first reinforcement-wall-forming elongated projections. Similarly, the reinforcement-wall-forming elongated projections 41 and 43 of a short projecting height of the upper and lower walls 31 and 32 are called the second reinforcement-wall-forming elongated projections. A groove 44 (45) is formed on the tip end face of the second reinforcement-wall-forming elongated projection 41 (43) of the upper wall 31 (lower wall 32) and extends in the longitudinal direction of the second reinforcement-wall-forming elongated projection 41 (43) along the entire length thereof. A tip end portion of the first reinforcement-wall-forming elongated projection 42 (40) of the lower wall 32 (upper wall 31) is fitted into the groove 44 (45) of the second reinforcement-wall-forming elongated projection 41 (43) of the upper wall 31 (lower wall 32). While tip end portions of the first reinforcement-wall-forming elongated projections 40 and 42 of the upper and lower walls 31 and 32, respectively, are fitted into the respective grooves 45 and 44, the reinforcement-wall-forming elongated projections 40 and 43 are brazed together, and the reinforcement-wall-forming elongated projections 41 and 42 are brazed together.

The heat exchange tube 4 is manufactured by use of a tube-forming metal sheet 50 as shown in FIG. 11(a). The tube-forming metal sheet 50 is formed, by rolling, from an aluminum brazing sheet having a brazing material layer on each of opposite sides. The tube-forming metal sheet 50 includes a flat upper-wall-forming portion 51 (flat-wall-forming portion); a flat lower-wall-forming portion 52 (flat-wall-forming portion); a connection portion 53 connecting the upper-wall-forming portion 51 and the lower-wall-forming portion 52 and adapted to form the rear side wall 34; the inner side-wall-forming elongated projections 37 and 38, which are integrally formed with the side ends of the upper-wall-forming and lower-wall-forming portions 51 and 52 opposite the connection portion 53 in an upward raised condition and which are adapted to form an inner portion of the front side wall 33; an outer side-wall-forming-elongated-projection forming portion 54, which extends outward from the side end of the upper-wall-forming portion 51 opposite the connection portion 53; and a plurality of reinforcement-wall-forming elongated projections 40, 41, 42, and 43, which are integrally formed with the upper-wall-forming and lower-wall-forming portions 51 and 52 in an upward raised condition and which are arranged at predetermined intervals in the width direction of the tube-forming metal sheet 50. The first reinforcement-wall-forming elongated projections 40 of the upper-wall-forming portion 51 and the second reinforcement-wall-forming elongated projections 43 of the lower-wall-forming portion 52 are located symmetrically with respect to the centerline of the width direction of the connection portion 53. Similarly, the second reinforcement-wall-forming elongated projections 41 of the upper-wall-forming portion 51 and the first reinforcement-wall-forming elongated projections 42 of the lower-wall-forming portion 52 are located symmetrically with respect to the centerline of the width direction of the connection portion 53. The projection 38 a is formed on the tip end face of the inner side-wall-forming elongated projection 38 of the lower-wall-forming portion 52, and the groove 37 a is formed on the tip end face of the inner side-wall-forming elongated projection 37 of the upper-wall-forming portion 51. The groove 44 (45), into which a tip end portion of the first reinforcement-wall-forming elongated projection 42 (40) of the lower-wall-forming portion 52 (upper-wall-forming portion 51) is fitted, is formed on the tip end face of the second reinforcement-wall-forming elongated projection 41 (43) of the upper-wall-forming portion 51 (lower-wall-forming portion 52).

The inner side-wall-forming elongated projections 37 and 38 and the reinforcement-wall-forming elongated projections 40, 41, 42, and 43 are integrally formed, by rolling, on one side of the aluminum brazing sheet whose opposite sides are clad with a brazing material, whereby a brazing material layer (not shown) is formed on the opposite side surfaces and tip end faces of the inner side-wall-forming elongated projections 37 and 38 and the reinforcement-wall-forming elongated projections 40, 41, 42, and 43; on the peripheral surfaces of the grooves 44 and 45 of the second reinforcement-wall-forming elongated projections 41 and 43; and on the vertically opposite surfaces of the upper-wall-forming and lower-wall-forming portions 51 and 52 and the outer side-wall-forming-elongated-projection forming portion 54.

The tube-forming metal sheet 50 is gradually folded at opposite side edges of the connection portion 53 by a roll forming process (see FIG. 11(b)) until a hairpin form is assumed. The inner side-wall-forming elongated projections 37 and 38 are caused to butt against each other; tip end portions of the first reinforcement-wall-forming elongated projections 40 and 42 are fitted into the respective grooves 45 and 44 of the second reinforcement-wall-forming elongated projections 43 and 41; and the projection 38 a is press-fitted into the groove 37 a.

Next, the outer side-wall-forming-elongated-projection forming portion 54 is folded along the outer surfaces of the inner side-wall-forming elongated projections 37 and 38, and a tip end portion thereof is deformed so as to be engaged with the lower-wall-forming portion 52, thereby yielding a folded member 55 (see FIG. 11(c)).

Subsequently, the folded member 55 is heated at a predetermined temperature so as to braze together tip end portions of the inner side-wall-forming elongated projections 37 and 38; to braze together tip end portions of the first and second reinforcement-wall-forming elongated projections 40 and 43; to braze together tip end portions of the first and second reinforcement-wall-forming elongated projections 42 and 41; and to braze the outer side-wall-forming-elongated-projection forming portion 54 to the inner side-wall-forming elongated projections 37 and 38 and to the lower-wall-forming portion 52. Thus is manufactured the heat exchange tube 4.

While opposite end portions of the heat exchange tubes 4 are inserted through the respective tube insertion holes 18 of the inside plates 8 and into the respective communication holes 22 of the intermediate plates 9 of the header tanks 2 and 3, and end surfaces of the opposite end portions abut the respective stepped portions 25 of the intermediate plates 9, the opposite end portions of the heat exchange tubes 4 are brazed to the respective peripheral wall surfaces of the tube insertion holes 18 of the inside plates 8 and to the respective peripheral wall surfaces of the communication holes 22 of the intermediate plates 9 by utilization of the brazing material layers of the inside plates 8 and the brazing material layers of the tube-forming metal sheets 50. That is, the entire outer peripheral surfaces of opposite end portions of the heat exchange tubes 4 are brazed to the respective entire peripheral wall surfaces of the tube insertion holes 18 of the inside plates 8 of the two header tanks 1 and 2, and at least opposite-side surfaces, extending in the tube-width direction (front-rear direction), of the entire outer peripheral surfaces of opposite end portions of the heat exchange tubes 4 and at least opposite wall surfaces 22 a, extending in the hole-length direction (front-rear direction), of the entire peripheral wall surfaces of the communication holes 22 of the intermediate plates 9 of the two header tanks 1 and 2 are respectively brazed together.

Accordingly, right end portions of an upper-half group of heat exchange tubes 4 are connected to the first header tank 2 so as to communicate with the interior of the upper outwardly bulging portion 11A, and left end portions are connected to the second header tank 3 so as to communicate with the interior of the outwardly bulging portion 24. Also, right end portions of a lower-half group of heat exchange tubes 4 are connected to the first header tank 2 so as to communicate with the interior of the lower outwardly bulging portion 11B, and left end portions are connected to the second header tank 3 so as to communicate with the interior of the outwardly bulging portion 24.

Each of the corrugated fins 5 is made in a wavy form from a brazing sheet; herein, an aluminum brazing sheet, having a brazing material layer on each of opposite sides.

The gas cooler 1 is manufactured by the steps of: preparing the aforementioned two provisional assemblies to be manufactured into the header tanks 2 and 3, a plurality of the aforementioned folded members 55, and a plurality of corrugated fins 5; arranging the two provisional assemblies in such a manner as to be spaced apart from each other with the inside plates 8 facing each other; arranging alternately the folded members 55 and the corrugated fins 5; inserting opposite end portions of the folded members 55 through the respective tube insertion holes 18 of the inside plates 8 and into the respective communication holes 22 of the intermediate plates 9 of the two provisional assemblies, and causing the end surfaces of the opposite end portions to abut the respective stepped portions 25 of the intermediate plate 9; arranging the side plates 6 externally of the respective opposite-end corrugated fins 5; arranging the inlet member 13 and the outlet member 16 on the outwardly bulging portions 11A and 11B, respectively, of the outside plate 7 used to form the first header tank 2; and brazing necessary portions of the provisional assemblies as mentioned above to thereby form the header tanks 2 and 3, brazing necessary portions of the folded members 55 as mentioned above to thereby form the heat exchange tubes 4, brazing the heat exchange tubes 4 to the header tanks 2 and 3, brazing the corrugated fins 5 to the heat exchange tubes 4, brazing the side plates 6 to the respective corrugated fins 5, and brazing the inlet member 13 and the outlet member 16 to the outwardly bulging portions 11A and 11B, respectively.

The gas cooler 1, together with a compressor, an evaporator, a pressure-reducing device, and an intermediate heat exchanger for performing heat exchange between a refrigerant from the gas cooler and a refrigerant from the evaporator, constitutes a supercritical refrigeration cycle. The refrigeration cycle is installed in a vehicle, for example, in an automobile, as a car air conditioner.

As shown in FIG. 12, in the gas cooler 1 described above, CO₂ from a compressor flows through the refrigerant inflow channel 14 of the inlet member 13 and enters the upper outwardly bulging portion 11A of the first header tank 2 through the refrigerant inlet 12. Then, the CO₂ dividedly flows into the refrigerant channels 4 a of all the heat exchange tubes 4 in communication with the upper outwardly bulging portion 11A. The CO₂ in the refrigerant channels 4 a flows leftward through the refrigerant channels 4 a and enters the outwardly bulging portion 24 of the second header tank 3. The CO₂ in the outwardly bulging portion 24 flows downward through the interior of the outwardly bulging portion 24 and through the communication portions 23 of the intermediate plate 9; dividedly flows into the refrigerant channels 4 a of all the heat exchange tubes 4 in communication with the lower outwardly bulging portion 11B; changes its course; flows rightward through the refrigerant channels 4 a; and enters the lower outwardly bulging portion 11B of the first header tank 2. Subsequently, the CO₂ flows out of the gas cooler 1 via the refrigerant outlet 15 and the refrigerant outflow channel 17 of the outlet member 16. While flowing through the refrigerant channels 4 a of the heat exchange tubes 4, the CO₂ is subjected to heat exchange with the air flowing through the air-passing clearances in the direction of arrow X shown in FIGS. 1 and 12, thereby being cooled.

In the above-described embodiment, the heat exchanger of the present invention is applied to a gas cooler of a supercritical refrigeration cycle. However, the heat exchanger of the present invention may be applied to an evaporator of the above-mentioned supercritical refrigeration cycle. This evaporator, together with a compressor, a gas cooler, a pressure-reducing device, and an intermediate heat exchanger for performing heat exchange between a refrigerant from the gas cooler and a refrigerant from the evaporator, constitutes a supercritical refrigeration cycle which uses a supercritical refrigerant such as CO₂. This refrigeration cycle is installed in a vehicle, for example, in an automobile, as a car air conditioner.

Although CO₂ is used as a supercritical refrigerant of a supercritical refrigeration cycle in the above-described embodiments, the refrigerant is not limited thereto, but ethylene, ethane, nitrogen oxide, or the like may be alternatively used.

The above-described embodiment uses, for forming the heat exchange tube 4, a folded member 55 which is formed by bending a tube-forming metal sheet in the form of an aluminum brazing sheet having a brazing material layer on each of opposite sides. However, the present invention is not limited thereto. For example, an aluminum extrudate having a brazing material layer on its outer surface may be used to form the heat exchange tube 4. 

1. A heat exchanger comprising a pair of header tanks disposed apart from each other and a plurality of flat heat exchange tubes disposed in parallel at intervals between the two header tanks and having opposite end portions connected to the respective header tanks, each of the two header tanks being configured such that an outside plate, an inside plate, and an intermediate plate intervening between the outside and inside plates are brazed together in layers, the outside plate having an outwardly bulging portion extending in a longitudinal direction thereof and having an opening closed by the intermediate plate, the inside plate having a plurality of tube insertion holes in the form of through-holes formed in a region corresponding to the outwardly bulging portion of the outside plate and spaced apart from one another along a longitudinal direction thereof, and the intermediate plate having a plurality of communication holes in the form of through-holes formed for allowing the respective tube insertion holes of the inside plate to communicate with the interior of the outwardly bulging portion of the outside plate, wherein a pair of inclined portions inclined in a fanning-out fashion toward the inside plate are formed at inside-plate-side edge portions of opposite wall surfaces of each communication hole of the intermediate plate which extend in a hole-length direction of the communication hole; a pair of projecting portions projecting toward the intermediate plate are formed on a surface of the inside plate which faces the intermediate plate, the projecting portions being located at positions corresponding to opposite edges of each tube insertion hole which extend in a hole-length direction of the tube insertion hole and being in close contact with the corresponding inclined portions of the intermediate plate; and the projecting portions are brazed to the corresponding inclined portions.
 2. A heat exchanger according to claim 1, wherein opposite end portions of the heat exchange tubes are inserted through the respective tube insertion holes of the inside plates and into the respective communication holes of the intermediate plates of the two header tanks; entire outer peripheral surfaces of opposite end portions of the heat exchange tubes are brazed to the respective entire peripheral wall surfaces of the tube insertion holes of the inside plates; and at least opposite-side surfaces, extending in a tube-width direction, of the entire outer peripheral surfaces of opposite end portions of the heat exchange tubes and at least opposite wall surfaces, extending in the hole-length direction, of the entire peripheral wall surfaces of the communication holes of the intermediate plates are respectively brazed together.
 3. A heat exchanger according to claim 1, wherein a hole width of the tube insertion hole of the inside plate and a hole width of the communication hole of the intermediate plate are equal.
 4. A heat exchanger according to claim 1, wherein Wp≦(Wt+0.8) and Hp≦(Ht+0.3) are satisfied, where Wp (mm) is a dimension of the communication hole of the intermediate plate as measured in the hole-length direction, Hp (mm) is a dimension of the communication hole of the intermediate plate as measured in a hole-width direction, Wt (mm) is a tube width of the heat exchange tube, and Ht (mm) is a tube height of the heat exchange tube.
 5. A heat exchanger according to claim 1, wherein the projecting portions of the inside plate are formed by bending, toward the intermediate plate, portions of the inside plate corresponding to opposite edges of each tube insertion hole which extend along in the hole-length direction of the tube insertion hole.
 6. A heat exchanger according to claim 1, wherein stepped portions are formed on a peripheral wall surface of each communication hole of the intermediate plate to be located at opposite end portions of the communication hole with respect to the hole-length direction, the stepped portions projecting inward with respect to the hole-length direction and engaging an end surface of the corresponding heat exchange tube.
 7. A heat exchanger according to claim 6, wherein a projecting height of each stepped portion of the intermediate plate from the peripheral wall surface of the corresponding communication hole is determined so as not to cover a refrigerant channel of the corresponding heat exchange tube.
 8. A heat exchanger according to claim 1, wherein each heat exchange tube is brazed to a peripheral wall surface of the corresponding communication hole of the intermediate plate by use of a brazing material on an outer peripheral surface of the heat exchange tube.
 9. A heat exchanger according to claim 8, wherein the heat exchange tube comprises a pair of flat walls facing each other and two side walls each extending between opposed side edges of the two flat walls and is formed by bending a tube-forming sheet-like member in the form of an aluminum brazing sheet having a brazing material layer on each of opposite sides. 